1. Field of the Invention
The present invention relates to method and apparatus for measuring blood sugar value in a living body under non-invasion condition.
2. Description of the Related Art
In order to set up a standard of the dose of insulin to control the blood sugar value (generally, the concentration value of glucose in blood) of a diabetic, a frequent (for example, several times per day) measurement of blood sugar value is required to be applied to the diabetic. It gives a heavy anguish to a patient to gather blood from the patient every time the measurement is carried out. Therefore, it has been required to measure the blood sugar value of a patient without actually gathering blood from the patient, that is, under non-invasion condition. In order to satisfy this requirement, there is proposed a method of irradiating infrared ray to a part being measured of a patient such as an earlobe, a finger or the like of the patient, detecting the infrared ray transmitted through the part being measured to measure the infrared ray absorption level of the part being measured. According to this method, an absorbance value which relatively accurately reflects the infrared ray absorption by glucose in the part being measured can be obtained by properly selecting the wavelength of the infrared ray being used, and the blood sugar value is determined on the basis of the absorbance value thus obtained.
In the optical blood sugar value measurement under non-invasion condition as described above, the condition of the part being measured (the optical path of infrared ray passing through the part being measured or the like) is varied due to the effect of pulsation or the like, and thus the measurement is unavoidable from accompanying some error due to the above variation. Therefore, it has been strongly required to reduce the measurement error as much as possible.
As a method of reducing the measurement error, it has been indicated that the blood sugar value may be determined, not by measuring the blood sugar value from the absorbance itself, but by using a secondary differential value of the absorbance (Japanese Patent Application Laid-open No. Hei-5-176917). According to this method, the measurement of absorbance is performed by using three wavelengths which are different from one another, but near to one another, and the variation corresponding to the secondary differential calculated through addition and subtraction of the absorbance values thus measured (the secondary differential value of absorbance) is used to determine the blood sugar value.
In the above optical non-invasion blood sugar value measuring method, there is an effect of infrared ray absorption by the components constituting the human body other than blood, and thus it is remarkably preferable to sufficiently remove this effect from the viewpoint of reducing the measurement error.